Adaptation to oscillopsia - A psychophysical and questionnaire investigation

In this study we explore the reasons why patients with bilateral vestibular failure report disparate degrees of oscillopsia, Twelve bilateral labyrint hine-defective (LD) subjects and twelve norm:al healthy controls were teste d using a self- versus visual-motion psychophysical experiment. The LD subj ects also completed a questionnaire designed to quantify the severity of ha ndicap caused by oscillopsia. Additional standardized questionnaires were c ompleted to identify the role of personality, personal beliefs and affectiv e factors in adaptation to oscillopsia. During the psychophysical experimen t subjects sat on a motorized Barany chair whilst viewing a large-field pro jected video image displayed on a screen in front of them. The chair and vi deo image oscillated sinusoidally at 1 Hz in counterphase at variable ampli tudes which were controlled by the subject but constrained, so that the net relative motion of the chair and video image always resulted in a sinusoid with a peak velocity of 50 degrees/s. The subject's task was to find the r atio of chair versus video image motion that subjectively produced the 'mos t comfortable visual image'. Eye movements were recorded during the experim ent in order that the net retinal image slip at the point of maximum visual comfort could be measured. The main findings in the LD subjects were that, as a group, they selected lower chair motion amplitude settings to obtain visual comfort than did the normal control subjects. Responses to the quest ionnaires highlighted considerable variation in reported handicap due to os cillopsia, Greater oscillopsia handicap scores were significantly correlate d with a greater external locus of control (i.e. the perception of having l ittle control over one's health), Retinal slip speed was negatively correla ted with oscillopsia handicap score so that patients who suffered the great est retinal slip were those least handicapped by oscillopsia. The results s uggest that adaptation to oscillopsia is partly related to the patient's pe rsonal attitude to the recovery process and partly associated with the deve lopment of tolerance to the movement of images on the retina during self-mo tion. The latter is likely to be related to previously described changes in visual motion sensitivity in these patients.